1. Field of the Invention
The present invention relates generally to methods of manufacturing semiconductor devices and, more specifically, to methods of patterning an electrical contact with different generations of lithography systems.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Semiconductor devices typically include a stratum of patterned layers. While each of the layers may serve different functions and comprise different materials, many of these layers are typically manufactured by performing some variant of three basic steps. First, a constituent material or materials are deposited on a substrate or underlying layer. Then, lithographic techniques are employed to form a patterned masking layer over the constituent materials. Finally, the underlying constituent materials that are exposed through the patterned masking layer are removed, thereby transferring the pattern of the masking layer to the constituent materials. To build a semiconductor device, this sequence of the steps is typically repeated a number of times to build up a series of layers.
Typically, lithography systems are employed to form the patterned masking layer. Generally, the lithography system applies a photoresist that chemically reacts when exposed to electromagnetic energy, such as ultraviolet light. After applying the photoresist, the photolithography system is employed to project an image corresponding to the desired pattern onto this layer of photoresist, through a photomask, for example. The image selectively exposes portions of the photoresist to electromagnetic energy, thereby causing these areas to chemically react and take on new properties. Generally, the photolithography system is used to develop the photoresist by selectively removing either areas of photoresist that were exposed to electromagnetic energy, in the case of a positive photoresist, or selectively removing areas of the resist that were not exposed to electromagnetic energy, in the case of negative photoresist. The resulting photorsists pattern forms a masking layer that generally corresponds to the image projected onto the photoresist.
Usually, it is important for the lithography system to precisely align to underlying layers before patterning the photoresist. For example, a vertical electrical contact between layers (hereinafter “contact”) typically should align with some conductive feature (or “target conductor”) in an underlying layer. Similarly, an electrical interconnect in the layer above the contact typically should align with that contact. In the present example, if each layer is properly aligned, the resulting contact will normally conduct current between the electrical interconnect and the target conductor. To this end, the photolithography system that patterns these features typically aligns with underlying layers before patterning the photoresist. Indeed, to facilitate alignment of layers, certain layers often include alignment marks. Generally, lithography systems patterning subsequent layers align to these marks before exposing the photoresist to electromagnetic radiation.
Often, to reduce costs, a single semiconductor manufacturing line will employ multiple generations of lithography systems. Typically, newer generations of lithography systems are much more expensive than older generation lithography systems. Thus, the capital equipment costs of a manufacturing line can typically be lowered by performing manufacturing steps on older generation lithography systems instead of newer generation lithography systems. At the same time, the newer generations of lithography systems are generally capable of patterning smaller features with tighter tolerances and more precise alignment to underlying layers than older generation lithography systems. As a result of these competing concerns of cost and performance, in a typical manufacturing line, the newer generation lithography systems are often reserved for critical layers, while the older generation lithography systems pattern less critical layers with larger features and less exacting tolerances.
Aligning the various layers in a semiconductor device presents difficulties in a manufacturing line that includes multiple generations of lithography systems. Unfortunately, it is difficult to precisely align the older generation lithography systems to layers patterned by the newer generation lithography systems. Consequently, when a contact and a target conductor are patterned with different generations of lithography systems, manufacturing lines may suffer lower yields due to misalignment of the contacts and the target conductors. Thus, there is a need for a method of electrically connecting a layer formed with an older generation lithography system to a layer formed with a newer generation lithography system.